Face seals are being used to eliminate leakage that often arises from improper use or other deficiencies of fittings that rely on metal-to-metal sealing. A typical face seal fitting includes a fitting body having a center bore that opens to a transverse sealing face. The outer periphery of the fitting body often is provided with external threads while the sealing face has formed therein an annular groove for containing an annular seal such as an elastomeric O-ring seal. The annular seal usually has an axial dimension greater than the depth of the groove so as to project from the sealing face. Accordingly, the annular seal will be compressed in the groove upon being engaged by a confronting sealing surface of a mating part.
In face seal tube fittings, elastomeric O-ring seals have been retained in the sealing face grooves by an interference fit usually at the outer diameter of the O-ring seal. Although this has proven to be adequate for the smaller tube fitting sizes, the larger tube fitting sizes have for a long time been plagued by the problem of the O-ring seal falling out of the groove. This problem in part is attributable to outer diameter variations of the larger O-ring seal sizes and in part to the slenderness of the larger diameter O-ring seals made of Buna-N rubber and the like. One disadvantage arising from this falling out problem is that the O-ring seals often become separated from the fittings during handling. The same problem and associated disadvantages no doubt plague other types of fittings and devices including face seals.
To overcome this problem it has been recommended that a dovetail groove be machined so that the O-ring is trapped by the converging sidewalls of the groove. This recommendation has not been widely accepted, since it is quite expensive to machine such dovetail grooves. Further attempts to retain the O-ring in its groove prior to assembly involve the use of an adhesive or grease to secure the O-ring within the groove. Extreme care must be exercised in using adhesives, since the member and the groove must be maintained in a clean condition for the adhesive to function, and grease does not provide a secure bond between the O-ring and the groove. Furthermore, grease and adhesives tend to pick up foreign matter and such foreign matter may interfere with the seal, particularly if it is present on the face of the member. Moreover, the necessary hand operations add to the cost of manufacturing.
In U.S. Pat. No. 3,831,951 there is described a technique that provides an O-ring groove which traps the O-ring in place. The O-ring groove is manufactured by first machining an O-ring groove in the flat face of a member and around an area to be sealed. At least one of the sidewalls of the groove so formed is deformed into the groove so that it forms an acute angle with the bottom wall of the groove and so that an upper lip of the deformed sidewall is spaced from the bottom wall a distance which exceeds the sectional radius of the O-ring and which defines a circle having a diameter less than the outside diameter but greater than the inside diameter of an O-ring to be inserted in the groove. When the O-ring is inserted in the groove, it is trapped by the deformed sidewall.
Several techniques for accomplishing the deforming operation are described in the '951 patent. A problem with these techniques is that they do not lend themselves to providing a continuous planar sealing face adjacent the deformed sidewall of the groove. This is particularly disadvantageous in high pressure applications when the lip of the deformed sidewall is on the sealing side of the groove, which is typically at the outer diameter of the groove in high pressure face seal fittings.